The present disclosure relates to a method and to a circuit for the improved use of a capacitance in an intermediate circuit. In particular, the present disclosure relates to intermediate circuits for on-board automobile energy systems in which voltage ripples can occur on a line between an energy store and an inverter at the engine.
The increased electrification of the individual traffic has led to the fact that in electrically drivable vehicles, distinctly higher voltages occur (in the 400 V range and higher) and must be processed, than have occurred in on-board vehicle systems until a few years ago. Whilst energy is stored as direct voltage in a (mostly electrochemical) energy store, an inverter is mostly used (direct-voltage/alternating-voltage converter) for supplying the electrical motor (or generator) with (three-phase) alternating voltage or transferring alternating voltage from the (generator-driven) motor into the electrochemical energy store. By means of the inverter, which frequently comprises AC/DC converters, a disturbance is superimposed on the on-board system voltage in the form of an alternating voltage which can lead to disturbances in the on-board system and to problems of electromagnetic compatibility (EMC). In order to attenuate the disturbance generated by the inverter, a so-called intermediate circuit capacitance is frequently provided between the energy store and the inverter which, when an increased voltage is present, receives energy, and thus “cushions” the voltage peak and, in the case of a voltage dip, delivers electrical energy and thus “boosts” the on-board system. Such a system is shown in FIG. 1. A battery 200 is connected via a so-called contactor 201, 202 to an inverter 203. An intermediate circuit capacitance C0 is connected in parallel with the input of the inverter 203 and the battery 200. The inverter 203 converts the high-voltage direct voltage into a three-phase alternating voltage with which an electric motor 204 is supplied. The intermediate circuit capacitor C0 has the task of attenuating the alternating-voltage components caused by the inverter on the direct-voltage side of the inverter. In the area of the automobile drive technology, such a capacitor usually has a capacitance of 0.5 to 1.5 mF and is very large and costly because of the required dielectric strength of over 400 V.
Furthermore, an active circuit for providing a predefined input impedance according to FIG. 2 is known in which a first operational amplifier 301 and a second operational amplifier 302, in conjunction with a voltage divider consisting of impedances Z1, Z2, Z3, Z4 and Z5, provide a predefined input impedance Zin=(Z1×Z2×Z3)/(Z2×Z4). Since the operation and action of the circuit shown in FIG. 2 is known to the expert, they will not be discussed in further detail.
It is an object of the present disclosure to reduce the costs and the size and the weight of a component used as intermediate circuit capacitance.